The present invention relates to a muffler for internal-combustion engine exhaust gases and a method of assembling the same, and, in particular, small mufflers for small appliance motors, such as motor saws and the like, having a housing which is essentially composed of two shell parts as well as passage bores for fastening screws arranged in the housing for holding the muffler at the internal-combustion engine, with only the shell part on the engine side being screwed to the engine.
In the case of a small muffler of this type shown in FIGS. 1 and 2 of DE-GM 76 04 869, the heads of the fastening screws hold the engine-side shell part on the cylinder head of the engine and are arranged inside the muffler. Thus, the screws are accessible only after the shell part facing away from the engine is demounted, this part being held at the engine-side shell part by screws.
In addition, FIG. 6 of DE-GM 76 04 869, as well as the GB-PS 14 47 877, show a muffler in which the fastening screws penetrate the muffler housing such manner that the screwheads rest on the exterior side facing away from the engine of the shell part which faces away from the engine, and the threaded parts of the screws projecting out of the engine-side shell part are screwed into engine-side threaded bores arranged there. This arrangement has the advantage that the fastening screws, in contrast to the known embodiment discussed above, can be mounted easily. Under certain circumstances, however, the fastening screws as well as the muffler housing are subjected to considerable temperatures, with the additional difficulty that the thermal stressing of the muffler housing the fastening screws may differ extensively depending on the engine load. Severe temperature changes must be correspondingly expected, and these changes necessarily have the result that the elements of the muffler housing and the fastening screws change their dimensions in correspondence with the respective temperature. Under certain circumstances, considerable mechanical distortions may therefore occur. After an extended use of the device, the seat of the fastening screw may become loose, for example, because the muffler housing was deformed as a result of strong mechanical tensions or because elastic intermediate elements are overstrained.
It is therefore an object of the present invention to provide a muffler and a method of assembly the muffler whose fastening screws, on one hand, are easily accessible and, on the other hand, can withstand extremely high thermal stress. At the same time, it is another object to make possible a simple construction and a simple mounting of the muffler.
According to the present invention, the foregoing objects are achieved by a construction and assembly method which makes the fastening screws accessible from the housing side formed by the shell part facing away from the engine, through pipes penetrating the housing. The pipe end, in the vicinity of the assigned passage bore, is held at the engine-side shell part, and the other pipe end forms an opening penetrating the shell part facing away from the engine.
As a result of the construction and assembly method and assembly method of the muffler according to the present invention, the heads of the fastening screws may be sunk in the housing, in which case the screwheads, from the direction of the interior side of the engine-side shell part, are braced against that shell part without stressing the other shell part. Because of this method of construction, extremely short fastening screws are sufficient because the changes of dimensions caused by temperature fluctuations are practically negligible. The heads of the fastening screws always remain accessible through the pipes without requiring disassembly of the muffler housing.
In addition, it is an advantage of the present invention that the engine-side shell part can be braced in a practical manner directly between the screw heads and engine-side holding parts by the screws without any stressing by tension forces of the housing of the muffler. During the mounting, the flexibility of the muffler housing, therefore, does not have to be taken into account in any way.
In a preferred embodiment of the present invention, a reinforcing bottom having openings arranged concentrically with respect to the passage bores rests on the interior side of the engine-side shell part. The pipes are held at this reinforcing bottom in a force-locking and/or form-fitting manner. In this manner, the shell part used for the fastening of the muffler can be reinforced in a simple way. At the same time, this construction offers the advantage that the reinforcing bottom may be assembled with the pipes before the connection of the reinforcing bottom and the shell part in order to facilitate the mounting of the pipes.
The connection of the shell part and of the reinforcing bottom may take place by pressure assembling. In this case, cup-type indentations are pressed into the sheets of the reinforcing bottom and the shell part which are disposed on top of one another. The cup edges of the indentations of the shell part and the reinforcing bottom engage in one another in a form-fitting and/or force-locking manner.
The openings of the reinforcing bottom which are concentric with respect to the passage bores of the fastening screws at the engine-side shell part may each have an edge which is flanged or folded over toward the interior of the housing and which, with the application of pressure, surrounds the pipe end assigned to the respective opening.
In a particularly advantageous embodiment of the present invention, each of the openings of the reinforcing bottom have an edge which is flanged or folded over in the direction to the interior of the housing with a funnel shape tapering in the direction of the interior. The ends of the pipes assigned to the reinforcing bottom each have a funnel shape fitting into the funnels of the reinforcing bottom such that the funnel-shaped pipe ends are form-fittingly--and in addition possibly also force-lockingly, held between the engine-side shell part and the funnel-shaped edges of the openings of the reinforcing bottom.
The pipe ends facing the engine-side shell part, in the direction of the pipe axis, may have flanged annular front faces, particularly such that the central openings remaining in the front faces have approximately the same diameter as the passage bores of the engine-side shell part arranged with the same axis. The annular front faces form a reinforcement of the surrounding areas of the passage bores of the engine-side shell part as well as a bearing surface for the heads of the fastening screws.
The open ends of the pipes penetrating the shell part facing away from the engine are preferably fitted into the openings of this shell part with the application of pressure. For this purpose, it is advantageously provided to taper or chamfer the exterior side of the pipe ends in the area of the shell part facing away from the engine in a funnel-shaped manner in the direction of the pipe ends such that the shell part facing away from the engine can be pushed with its openings onto the pipe ends with increasing pressure between the pipe ends and the opening edges.
A particularly significant advantage of the muffler construction and method according to the present invention is that the muffler housing can be completely assembled and form a stable unit before muffler elements are tightly soldered together with one another. Thus, by virtue of the reinforcing bottom which can be connected with the engine-side shell part by pressure-assembling, the pipes can be held at the shell part on the engine side. The shell part facing away from the engine is held at the ends of the pipes facing away from the engine by a press fit. Then the edges of the shell parts disposed on top of one another can be soldered together with one another; and the pipe ends are connected with the respective shell parts also by soldering.